Donor—acceptor interactions of substituted benzenes with molecular chlorine and carbon disulfide

CNDO molecular orbital calculations have been performed to analyze donor—acceptor interactions between molecular chlorine and benzene, toluene, mesitylene and hexamethylbenzene and the, as yet, unreported chlorine—hexafluorobenzene and carbon disulfide—benzene pairs. The stabilization energy and the dipole moment and its derivative (?p/?R_CICI) calculated for the benzene—chlorine complex are in good agreement with the estimated experimental values. The trends in the experimental stabilization energies and the Cl-Cl vibrational frequencies with increasing methyl substitution appear to be well reproduced by the calculations. The charge transferred from the benzene donor is polarized toward the outer chlorine atom or sulfur atom. For hexafluorobenzene-chlorine the direction of electronic charge polarization is reversed from that of the benzene and methylbenzene complexes. The calculated results are discussed within the framework of Muliiken's simplified resonance theory for complexes.     

Synthesis of 1,2-dihydroindolo [1,7-AB] [1,5] benzodiazepines and related structures. A new heterocyclic ring system

The synthesis of the novel 1,2-dihydroindolo [1,7-ab][1,5]benzodiazepine ring system 4 is described. Condensation of 2-fluoronitrobenzene with indoline provided the starting material for the synthesis, 1-(2-nitrophenyl)indoline (1a) in high yield. The nitro group was reduced catalytically and the resulting amino function was acylated to afford the heterocycle percursor amide 3. Refluxing this amide in phosphorus oxychloride brought about a Bischler-Napieralski type cyclodehydration to form the target 1,2-dihydroindolo[1,7-ab][1,5]benzodiazepine ring system. Dehydrogenation of the latter led to the fully aromatic indolo[1,7-ab][1,5]benzodiazepine structure 5, while reduction with sodium borohydride provided the 1,2,6,7-tetrahydroindolo[1,7-ab]-[1,5]benzodiazepine tetracycle 6.     

Ascorbate-induced oxidation of formate by peroxodisulfate: product yields,kinetics and mechanism

The slow reaction between peroxodisulfate and formate is significantly accelerated by ascorbate at room temperature. The products of this induced oxidation, CO₂ and oxalate (C₂O^2– ₄), were analyzed by several methods and the kinetics of this reaction were measured. The overall mechanism involves free radical species. Ascorbate reacts with peroxodisulfate to initiate production of the sulfate radical ion (SO^– ₄), which reacts with formate to produce carbon dioxide radical ion (CO^– ₂) and sulfate. The carbon dioxide radical reacts with peroxodisulfate to form CO₂ or self-combines to form oxalate. Competition occurring between these two processes determines the overall fate of the carbon dioxide radical species. As pH decreases, protonation of the carbon dioxide radical ion tends to favor production of CO₂.     

SPECTRAL CHARACTERISTICS AND MECHANISM OF CHEMILUMINESCENCE FROM TRYPTOPHAN SOLUTIONS INDUCED BY UV-IRRADIATION

The spectral distribution of the chemiluminescence, fluorescence and phosphorescence of tryptophan aqueous solutions irradiated with high and low pressure mercury lamps has been measured. The blue emission bands in the region of 380–520 nm observed both in the chemi- and photoluminescence, as well as an absorbance increase at 230 and 330 nm, indicate oxidative degradation of tryptophan leading to the formation of derivatives of N-formylkynurenine, xanthurenic and anthranilic acids. Red emission bands at 630 and 705 nm in the spectrum of the chemiluminescence, an enhancement of light intensity by D₂O and its decrease by NaN₃ and DABCO suggest a partial contribution of O₂(¹Δ_g) to the photooxidation and chemiluminescence of tryptophan. The enthalpy of the exergonic reactions, leading to the formation of luminescing products, was calculated to average -270 kJ-mol.     

Cyclopentadienyl-ruthenium and -osmium chemistry: XXVIII. Reactions and isomerisation of 1,2-bis(methoxycarbonyl)ethenyl complexes: X-ray structures of Ru{Z)-C(CO2Me)CH(CO2Me)} -(CO)(PPh3)(η-C5H5) · 0.5EtOH,Ru{(E)-C(CO2Me)CH(CO2Me)}(dppe)(η-C5H5) and Ru{C(CO2Me)C(CO2Me)C(CO2Me)CH(CO2Me)} - (PPh3)(η-C5H5)

A reinvestigation of the reaction between C₂(CO₂Me)₂ and RuH(PPh₃)₂(η-C₅H₅) and some related complexes is reported. Initial cis addition is followed by conversion into the trans isomer. In the case of the bis-(PPh₃) complex, isomerisation is followed by chelation of the ester CO group with concomitant displacement of one PPh₃ligand. The resulting chelate complex reacts with CO or CNBu^t to give the (Z)-RuC(CO₂Me)CH(CO₂Me) complexes; the (E)-isomer of the carbonyl complex is obtained by addition of C₂(CO₂Me)₂to RuH(CO)(PPh₃)(η-C₅H₅). The ^1Hand ¹³C NMR spectra are not a reliable guide to assignment of the stereochemistry of the vinyl group. Other products isolated from the initial reaction are the bis-insertion product $\text{Ru{C(CO}{}_2\text{Me)C(CO}{}_2\text{Me)C(CO}{}_2\text{Me)}$CH(CO₂Me)} -(PPh₃)(η-C₅H₅) and the 1/2 PPh₃/C₂(CO₂Me)₂ adduct. The molecular structures of Ru{(Z)-C(CO₂Me)CH(CO₂Me)}(CO)(PPh₃(η-C₅H₅) · 0.5EtOH, Ru{(E)-C(C₂Me)CH(CO₂Me)}(dppe)(η-C₅H₅) and $\text{Ru{C(CO}{}_2\text{Me)C(CO}{}_2\text{Me)C(CO}{}_2\text{-Me)}$CH(CO₂Me)}(PPh₃)(η-C₅H₅) have been determined. The cis isomer is monoclinic, space group P2₁,with a 9.328(8), b 17.385(10), c 10.356(7) Å, β 101.78(3)° and Z = 2; 2107 data with I ≥ 2.5σ(I) were refined to R = 0.076 R_w = 0.085. The trans isomer is triclinic, space group P$\text{1}$, with a 10.404(7) b 11.221(6), c 13.230(9) Å, α 92.67(5), β 110.56(5), γ 106.21(5)° and Z = 2; 2520 data with I ≥ 2.5σ(I) were refined to R = 0.055 R_w = 0.068. The butadienyl complex is monoclinic, space group P2₁/a, with a 19.655(8), b 8.674(4), c 21.060(5) Å, β 116.22(3)° and Z = 4; 2724 data with I ≥ 2.5σ(I) were refined to R = 0.042, R_w = 0.047.     

Quinazolines. VII. Synthesis of 1,3-Diamino-5,6-dihydrobenzo[f]quinazolines

Eighteen new 1,3-diamino-5,6-dihydrobenzo[f] quinazolines ( 6 , R. = alkyl, Cl, MeO) were synthesized via the condensation of appropriate 2-tetralones with cyanoguanidine under fusion conditions. Methods were developed for the preparation of a number of heretofore undescribed 2-tetralones as precursors. The final products can be viewed as conformationally rigid analogs of pyrimethamine ( 2 ), and are of interest as inhibitors of dihydrofolate reductase and as potential antimalarial and antitumor agents.     

Unusual reactivity of ortho-carbonylphenylboronic acids with diethanolamine

The reaction of carbonyl-substituted phenylboronic acids with diethanolamine has been investigated. For compounds containing carbonyl groups at the meta or para positions the reaction occurs exclusively at the boronic acid. Different reactivities were observed for ortho-substituted acetyl- and formylphenylboronic acids where the reaction occurred at both the boronic acid and at the carbonyl group. X-ray studies revealed the presence of a polycyclic structure with tetravalent boron and nitrogen atoms.     

Detection of DNA fragments separated by capillary electrophoresis based on their native fluorescence inside a sheath flow

A scheme for the separation and detection of native DNA fragments in capillary electrophoresis is presented. A UV laser at 275 nm excites the intrinsic fluorescence of the fragments, which is greatly enhanced at pH 2.8. To provide a compatible system, methylcellulose-based size separation is performed at the identical pH. A sheath-flow arrangement isolates the detection region from the linear polymer for a reduced background level. The performance is an order-of-magnitude enhancement in detectability over absorption detection. We also uncovered a selective degradation/ligation process at these pH conditions that may be useful as additional selectivity for DNA characterization.     

New 2+2, 3+3 and 4+4 macrocycles derived from 1,2-diaminocyclohexane and 2,6-diformylpyridine

Two new Schiff base macrocycles - a 4+4 condensation product and a meso-type 2+2 condensation product - were obtained in a reaction of trans-1,2-diaminocyclohexane and 2,6-diformylpyridine. Reduction of these compounds led to the corresponding 4+4 and 2+2 macrocyclic amines. The macrocycles were characterised by NMR spectroscopy and electrospray mass spectrometry. The symmetry and stereochemistry of these macrocycles, as well as of new 3+3 and 4+4 diastereomers identified in solution, has been established. X-Ray structures of the 2+2 and 4+4 Schiff base macrocycles confirm the configurations determined on the basis of spectroscopic investigations. The crystal structures reveal that the centres of the square-shaped 4+4 macrocycles form channels as a result of columnar stacking.